Over one half million total knee replacement (TKR) surgeries are performed in the United States every year. This number is expected to grow to over three-and-a-half million surgeries by the year 2030. In recent years, significant progress has been made in the surgical procedure, surgical components, and approaches to rehabilitation. Initially, TKR patients were immobilized for 4 to 6 weeks following surgery because it was feared that early range of motion (ROM) movements would be harmful to the new joint. The result, however, was that regaining full ROM was extremely difficult after the knee was immobilized for one month. Nevertheless, for many severely afflicted individuals, this was felt to be an acceptable tradeoff for a pain free gait.
Gradually, medical practitioners began to recognize that early ROM was preferable and generated better results. Indeed, knee ROM was easier to restore and knee bend ranges were improved. To take advantage of this recognition, a continuous passive motion (CPM) machine was developed. The CPM machine uses a mechanical force to bend the knee through a set ROM at a set speed. The patient is required to lie supine with his or her leg strapped within a frame. The CPM machine is then anchored to a bed using straps which prevent movement and slippage away from the patient during use.
Eventually, studies were created to examine the effectiveness of patients themselves bending the knee (active ROM) as opposed to the CPM machine doing the bending. It was concluded that active and active assisted ROM by the patient was just as effective at restoring ROM as the CPM machine. Nevertheless, the CPM machine is still used by some physicians to encourage ROM very early post operative while the patient is physically or mentally unable to actively participate in the rehabilitation process. Presently, conventional wisdom is that early and frequent active and active assisted range of motion by the patient is the best and most cost effective way to regain range of motion post surgery. In comparing various exercise methods to enhance ROM, it has been suggested that the actual method used does not matter. Most patients who are initially slow to regain range eventually catch up at 6 months or one year and that quality of life measures are similar one year after surgery. However, patients who get ROM back quickly spend less time on pain medication, less time dealing with side effects of the pain medication (such as constipation, drowsiness, and fear of addiction), can engage in community activities sooner, and overall, feel better about the surgery. Additionally, patients who do not regain early range may gain adequate range (a 90 degree knee bend from a straight leg), but are unlikely to gain excellent range (bending a straight leg at the knee 120 degrees or more, or a complete bend). All patients, but especially taller patients (above six feet tall), will be hindered by a knee range of 90 degrees or less. This limited range can adversely affect patient activity levels, safety, and future independence.
Despite advances in approach and technique in patient rehabilitation following total knee replacement, TKR continues to have a reputation as being a “tough” surgery. There are multiple reasons for this. Assuming adequate pain management, the top two reasons for failure to regain knee range of motion in a timely manner are 1) insufficient bio-mechanical advantage, and 2) insufficient frequency of exercise.
Bio-mechanical advantage is important in rehabilitation following a TKR because the knee is swollen and stiff. Typically, the hamstring on the affected side has weakened prior to surgery and may not be able to overcome the tissue tightness in the knee following surgery. Ways to compensate for the weak pull of the hamstring include using the unaffected side to assist in flexing the surgical knee, using human power like a physical therapist or family member, and using tools to leverage the knee bend (such as stairs or a loose strap to pull the knee into flexion). Troubles occur when one or several ways are not available to the patient on a regular basis. For example, the non-surgical knee may not be pain-free and might be weak as well, thereby eliminating the bio-mechanical advantage. Using other humans is a method that forces the patient to be dependent on someone else. A physical therapist may only be available three times a week or family members may not be available for most of the day or may not be willing or capable to assist the patient. Frustration results as the patient cannot be self-determining in the course of his or her rehabilitation. Relying on a set of stairs for exercises presents numerous safety issues, such as the stairs being cluttered or the patient losing his or her balance.
Thus, it is readily apparent that there is a long-felt need for a knee exercising device and method, particularly for patients following a total knee replacement surgical procedure.